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Turbulence and Shear Flow Phenomena -1 First International Symposium

ISBN:
1-56700-135-1 (Print)

INSTANTANEOUS AND FILTERED VELOCITY PROFILES IN SMOOTH AND ROUGH BOUNDARY LAYERS

Akihiko Nakayama
Department of Global Development Science, Graduate School of Science and Technology, Kobe University, Rokkodai, Nada-ku, Kobe 657-8501, Japan

Kazuhiro Maeda
Graduate School of Science and Technology Kobe University, Nada-ku, Kobe 657-8501, Japan

Hiroshi Noda
Graduate School of Science and Technology Kobe University, Nada-ku, Kobe 657-8501, Japan

Abstract

Instantaneous profiles of stream wise velocity component in the viscous and roughness sublayers and in the lower parts of the log-law region of flat-plate boundary layers over smooth and rough surfaces have been measured using a hot-wire rake consisting of two X-wire and nine single sensor probes in order to investigate the turbulence structure and similarity of instantaneous and filtered velocity profiles near wall. The results can provide supplemental relations for large-eddy type simulation of a large Reynolds number flows. The instantaneous velocity profiles are strongly influenced by the quasi-periodic large structures of the wall turbulence to exhibit universal similarity, but the filtered profiles normalized by the filtered instantaneous friction velocity show similarity that progressively extends from the region close to the wall to the log layer as the filter size is increased. The minimum streamwise length of the filter size required to show logarithmic similarity is found to be as large as 1800 wall units.